I don’t see the argument. Walmart and others are sucking while Bezos is executing.
Unless Bezos crosses the line with onerous contracts not allowing manufacturers to sell with other online retailers he should be ok. Wise for Bezos to put antitrust friendly language in all contracts.
When you choose to enroll your book in KDP Select, you're committing to make the digital format of that book available exclusively through KDP. During the period of exclusivity, you cannot distribute your book digitally anywhere else, including on your website, blogs, etc.
Related: If you include a link in an ePub to any other retailer, the book will be rejected by Amazon.
I don't know what world you're in, but Walmart is kicking ass as a company and is still posting a net profit larger than Amazon's, despite Amazon making boats of money off of AWS. At this point people prefer shopping at Walmart to Amazon.